Piezoelectric device and method of manufacturing piezoelectric device

ABSTRACT

A piezoelectric device includes a piezoelectric body at least a portion of which can bend and vibrate, an upper electrode on an upper surface of the piezoelectric body and in which distortion of a crystal lattice is reduced as a distance from the upper surface of the piezoelectric body increases, a lower electrode on a lower surface of the piezoelectric body and in which distortion of a crystal lattice is reduced as a distance from the upper surface of the piezoelectric body increases, and a support substrate below the piezoelectric body, in which a recess extending from a lower surface of the support substrate toward the lower surface of the piezoelectric device is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2017-224543 filed on Nov. 22, 2017 and is a ContinuationApplication of PCT Application No. PCT/JP2018/042572 filed on Nov. 16,2018. The entire contents of each application are hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a piezoelectric device and a method ofmanufacturing a piezoelectric device.

2. Description of the Related Art

A vibrator having a unimorph structure or a bimorph structure, which isused for a clock oscillator, a piezoelectric buzzer, or the like, hasbeen developed. The unimorph structure has a laminated structureincluding a piezoelectric body and a passive elastic layer or apiezoelectric body to which a voltage is not applied. An upper electrodeis disposed on an upper portion of the piezoelectric body, and a lowerelectrode is disposed on a lower portion of the piezoelectric body. Whena voltage is applied to the piezoelectric body by using the upperelectrode and the lower electrode, the piezoelectric body tends toexpand and contract in an in-plane direction. However, since the passiveelastic layer or the piezoelectric body to which a voltage is notapplied does not expand and contract, the unimorph structure bends andvibrates. The bimorph structure is a laminated structure of two layersof piezoelectric bodies. An elastic plate such as a metal plate called ashim may be interposed between the two layers of piezoelectric bodies.When a voltage is applied to the two layers of piezoelectric bodies, onepiezoelectric body extends in the in-plane direction and anotherpiezoelectric body tends to contract in the in-plane direction, so thatthe two layers of piezoelectric bodies bend as a whole. Thepiezoelectric body is made of, for example, aluminum nitride (AlN), leadzirconate titanate (PZT), or the like (see, for example, Japanese PatentNo. 4404218 and Japanese Patent No. 6132022). The piezoelectric body isformed on the lower electrode by, for example, a vapor depositionmethod, a sputtering method, a laser ablation method, a chemical vapordeposition (CVD) method, or the like. Then, the upper electrode isformed on the piezoelectric body.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide piezoelectricdevices each having high reliability, and methods of manufacturing apiezoelectric device.

According to a preferred embodiment of the present invention, apiezoelectric device includes a piezoelectric body at least a portion ofwhich is capable of bending and vibrating, an upper electrode which isdisposed on an upper surface of the piezoelectric body and in whichdistortion of a crystal lattice is reduced as a distance from the uppersurface of the piezoelectric body increases, a lower electrode which isdisposed on a lower surface of the piezoelectric body and in whichdistortion of a crystal lattice is reduced as a distance from the lowersurface of the piezoelectric body increases, and a support substratedisposed below the piezoelectric body, in which a recess extending froma lower surface of the support substrate toward the lower surface of thepiezoelectric body is provided.

According to a preferred embodiment of the present invention, a methodof manufacturing a piezoelectric device in which at least a portion of apiezoelectric body is capable of bending and vibrating, includesdepositing a conductive material on a lower surface of the piezoelectricbody to form a lower electrode made of the deposited conductivematerial, depositing a conductive material on an upper surface of thepiezoelectric body to form an upper electrode made of the depositedconductive material, disposing a support substrate below thepiezoelectric body, and providing a recess extending from a lowersurface of the support substrate toward the lower surface of thepiezoelectric body.

According to preferred embodiments of the present invention,piezoelectric devices each having high reliability and methods ofmanufacturing a piezoelectric device are provided.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an upper perspective view illustrating a piezoelectric deviceaccording to a first preferred embodiment of the present invention.

FIG. 2 is a schematic perspective view illustrating the piezoelectricdevice according to the first preferred embodiment of the presentinvention, as viewed from a direction of a line II-II in FIG. 1.

FIG. 3 is a lower perspective view illustrating the piezoelectric deviceaccording to the first preferred embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view illustrating a method ofmanufacturing the piezoelectric device according to the first preferredembodiment of the present invention.

FIG. 5 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the first preferredembodiment of the present invention.

FIG. 6 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the first preferredembodiment of the present invention.

FIG. 7 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the first preferredembodiment of the present invention.

FIG. 8 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the first preferredembodiment of the present invention.

FIG. 9 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the first preferredembodiment of the present invention.

FIG. 10 is a schematic cross-sectional view illustrating a piezoelectricdevice according to the prior art.

FIG. 11 is a schematic cross-sectional view illustrating a piezoelectricdevice according to a second preferred embodiment of the presentinvention.

FIG. 12 is a schematic cross-sectional view illustrating a method ofmanufacturing the piezoelectric device according to the second preferredembodiment of the present invention.

FIG. 13 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the second preferredembodiment of the present invention.

FIG. 14 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the second preferredembodiment of the present invention.

FIG. 15 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the second preferredembodiment of the present invention.

FIG. 16 is a schematic cross-sectional view illustrating a piezoelectricdevice according to a third preferred embodiment of the presentinvention.

FIG. 17 is a schematic cross-sectional view illustrating a method ofmanufacturing the piezoelectric device according to the third preferredembodiment of the present invention.

FIG. 18 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the third preferredembodiment of the present invention.

FIG. 19 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the third preferredembodiment of the present invention.

FIG. 20 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the third preferredembodiment of the present invention.

FIG. 21 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the third preferredembodiment of the present invention.

FIG. 22 is a schematic cross-sectional view illustrating a piezoelectricdevice according to a fourth preferred embodiment of the presentinvention.

FIG. 23 is a schematic cross-sectional view illustrating a method ofmanufacturing the piezoelectric device according to the fourth preferredembodiment of the present invention.

FIG. 24 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the fourth preferredembodiment of the present invention.

FIG. 25 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the fourth preferredembodiment of the present invention.

FIG. 26 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the fourth preferredembodiment of the present invention.

FIG. 27 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the fourth preferredembodiment of the present invention.

FIG. 28 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the fourth preferredembodiment of the present invention.

FIG. 29 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the fourth preferredembodiment of the present invention.

FIG. 30 is a schematic cross-sectional view illustrating the method ofmanufacturing the piezoelectric device according to the fourth preferredembodiment of the present invention.

FIG. 31 is a schematic cross-sectional view illustrating a piezoelectricdevice according to a fifth preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. In thefollowing description of the drawings, the same or similar portions aredenoted by the same or similar reference numerals. However, the drawingsare schematic. Therefore, specific dimensions and the like should bedetermined by comparing the following description. In addition, each ofthe drawings includes portions in which mutual dimension relationshipsand ratios are different.

First Preferred Embodiment

A piezoelectric device according to a first preferred embodiment of thepresent invention includes, as illustrated in FIG. 1, which is an upperperspective view, FIG. 2, which is a schematic cross-sectional view asviewed from a direction of a line II-II in FIG. 1, and FIG. 3, which isa lower perspective view, a piezoelectric body 10 at least a portion ofwhich can bend and vibrate, an upper electrode 22 which is disposed onan upper surface of the piezoelectric body 10 and in which distortion ofa crystal lattice is reduced as a distance from the upper surface of thepiezoelectric body 10 increases, a lower electrode 21 which is disposedon a lower surface of the piezoelectric body 10 and in which distortionof a crystal lattice is reduced as a distance from the lower surface ofthe piezoelectric body 10 increases, and a support substrate 40 disposedbelow the piezoelectric body 10. The piezoelectric device includes arecess 141 extending from the lower surface of the support substrate 40toward the lower surface of the piezoelectric body 10.

The piezoelectric device according to the first preferred embodiment mayfurther include an amorphous layer 30 disposed on the lower surface ofthe piezoelectric body 10 and on the lower surface of the lowerelectrode 21. The support substrate 40 may be disposed on a lowersurface of the amorphous layer 30.

The piezoelectric body 10 is preferably made of, for example, a singlecrystal such as lithium tantalate (LT) lithium niobate (LN) or the like.The piezoelectric body 10 has a uniform film quality over a portion inwhich the lower electrode 21 is provided downward and a portion in whichthe lower electrode 21 is not provided downward, and has the samepolarization (orientation) state within the film. The upper surface andthe lower surface of the piezoelectric body 10 are flat and smoothexcept for portions which are processed for extraction electrodes,device formation, and the like, and does not include any steps andtapered structures. However, Total Thickness Variation (TTV) equal to orless than about 2 μm, for example, is acceptable.

The lower electrode 21 and the upper electrode 22 are preferably madeof, for example, a conductive material such as platinum (Pt), gold (Au)or the like. The lower electrode 21 and the upper electrode 22 arecapable of applying a voltage to the piezoelectric body 10. The lowerelectrode 21 and the upper electrode 22 have at least one kind oftriaxial texture. Due to misfit dislocation, the lower electrode 21 onthe side close to the piezoelectric body 10 is distorted in the crystallattice, and the lower electrode 21 is structured such that distortionof the crystal lattice is reduced as a distance from the piezoelectricbody 10 increases. Further, due to the misfit dislocations, the upperelectrode 22 on the side close to the piezoelectric body 10 is distortedin the crystal lattice, and the lower electrode 22 is such thatdistortion of the crystal lattice is reduced as a distance from thepiezoelectric body 10 increases. Therefore, crystallinity of the lowerelectrode 21 and the upper electrode 22 varies symmetrically with thepiezoelectric body 10 interposed therebetween.

In the piezoelectric device according to the first preferred embodiment,a lower adhesion layer which enables the piezoelectric body 10 and thelower electrode 21 to be in close contact with each other may beprovided between the piezoelectric body 10 and the lower electrode 21.The lower adhesion layer is preferably made of, for example, a metalsuch as titanium (Ti), chromium (Cr) or the like. At least a portion ofthe lower adhesion layer may be oxidized. In the piezoelectric deviceaccording to the first preferred embodiment, an upper adhesion layerwhich enables the piezoelectric body 10 and the upper electrode 22 to beclose contact with each other may be provided between the piezoelectricbody 10 and the upper electrode 22. The upper adhesion layer ispreferably made of, for example, a metal such as titanium (Ti), chromium(Cr) or the like. At least a portion of the upper adhesion layer may beoxidized.

The amorphous layer 30 is preferably made of, for example, an insulatingmaterial such as silicon oxide. The amorphous layer 30 may be a heatinsulating material. The lower electrode 21 is embedded in the amorphouslayer 30.

The support substrate 40 is preferably, for example, a silicon oninsulator (SOI) substrate including a handle layer 41, an embedded oxidefilm 42 disposed on the handle layer 41, and an active layer 43 disposedon the embedded oxide film 42. The lower surface of the amorphous layer30 and an upper surface of the active layer 43 of the SOI substrate arebonded to each other.

The embedded oxide film 42 may be exposed from a bottom surface 142 ofthe recess 141, the active layer 43 may be exposed, the amorphous layer30 may be exposed, or the piezoelectric body 10 and the lower electrode21 may be exposed.

In the first preferred embodiment, when viewed from above, a portion inwhich at least the upper electrode 22, the piezoelectric body 10, andthe lower electrode 21 overlap each other defines and functions as aflexural vibration membrane. When a voltage is applied to thepiezoelectric body 10 from the lower electrode 21 and the upperelectrode 22, the piezoelectric body 10 tends to expand and contract inthe in-plane direction, but at least the upper electrode 22 and thelower electrode 21 do not expand and contract, so that the flexuralvibration membrane bends and vibrates vertically.

Depending on a position of the bottom surface of the recess 141 providedin the piezoelectric device, the flexural vibration membrane may furtherinclude at least a portion of the amorphous layer 30. In addition, theflexural vibration membrane may further include at least a portion ofthe amorphous layer 30 and at least a portion of the active layer 43.Alternatively, the flexural vibration membrane may further include atleast a portion of the amorphous layer 30, at least a portion of theactive layer 43, and at least a portion of the oxide film 42. It ispreferable that a neutral plane within the flexural vibration membranebe located outside the piezoelectric body 10 when the flexural vibrationmembrane bends and vibrates.

In a case where the amorphous layer 30 is exposed from the bottomsurface of the recess 141, it is preferable that a thickness of theamorphous layer 30 is set such that the neutral plane is within theamorphous layer 30 and not within the piezoelectric body 10 when theflexural vibration membrane bends and vibrates.

In a case where the active layer 43 is exposed from the bottom surfaceof the recess 141, it is preferable that a total thickness of theamorphous layer 30 and the active layer 43 be set in a manner such thatthe neutral plane is within the amorphous layer 30 or the active layer43 and not within the piezoelectric body 10 when the flexural vibrationmembrane bends and vibrates.

In a case where the embedded oxide film 42 is exposed from the bottomsurface of the recess 141, it is preferable that a total thickness ofthe amorphous layer 30, the active layer 43, and the embedded oxide film42 is set such that the neutral plane is within the amorphous layer 30,the active layer 43, or the embedded oxide film 42, and not within thepiezoelectric body 10, when the flexural vibration membrane bends andvibrates.

Next, a non-limiting example of a method of manufacturing thepiezoelectric device according to the first preferred embodiment will bedescribed.

As illustrated in FIG. 4, a substrate piezoelectric body preferably madeof, for example, a single crystal such as lithium tantalate (LT),lithium niobate (LN) and the like is prepared, and a conductive filmpreferably made of, for example, a conductive material such as platinum(Pt), gold (Au) and the like is formed on a smooth and flat lowersurface of the piezoelectric body 15 by heteroepitaxial growth. Thelower electrode 21 is formed on a lower surface of the piezoelectricbody 15 by patterning the conductive film into a predetermined shape. Alower adhesion layer preferably made of, for example, a metal such astitanium (Ti), chromium (Cr) and the like may be formed on the lowersurface of the piezoelectric body 15, and then a conductive film may beformed on the lower adhesion layer.

As illustrated in FIG. 5, the amorphous layer 30 preferably made of, forexample, silicon dioxide (SiO₂) or the like is formed on the lowersurface of the piezoelectric body 15 and on the lower surface of thelower electrode 21. Accordingly, the lower electrode 21 is disposed inthe amorphous layer 30. Thereafter, the lower surface of the amorphouslayer 30 is subjected to chemical mechanical polishing (CMP) to smooththe lower surface of the amorphous layer 30.

As illustrated in FIG. 6, the SOI substrate including the handle layer41, the embedded oxide film 42 disposed on the handle layer 41, and theactive layer 43 disposed on the embedded oxide film 42 is prepared asthe support substrate 40. Next, as illustrated in FIG. 7, the uppersurface of the active layer 43 of the SOI substrate and the lowersurface of the amorphous layer 30 are directly bonded to each other.Thereafter, as illustrated in FIG. 8, the substrate piezoelectric body15 is polished from the upper surface side to be thinned, thus formingthe piezoelectric body 10 as a film. A thickness of the piezoelectricbody 10 is set such that a desired expansion and contraction occurs whena voltage is applied thereto.

As illustrated in FIG. 9, a conductive film preferably made of, forexample, a conductive material such as platinum (Pt), gold (Au) and thelike is formed on the upper surface of the piezoelectric body 10 by theheteroepitaxial growth. The conductive film is patterned in apredetermined shape to form the upper electrode 22 on a smooth and flatupper surface of the piezoelectric body 10. Alternatively, the upperadhesion layer preferably made of, for example, a metal such as titanium(Ti), chromium (Cr) and the like may be formed on the upper surface ofthe piezoelectric body 10, and then the conductive film may be formed onthe upper adhesion layer. Next, optionally, portions of the active layer43 of the SOI substrate, the amorphous layer 30, and the piezoelectricbody 10 may be removed by an etching method or the like, to be patternedinto a desired shape. For example, a wiring connected to the lowerelectrode 21 exposed by removing a portion of the piezoelectric body 10may be provided.

The recess 141 illustrated in FIG. 2 is formed in a portion of the lowersurface of the handle layer 41 of the SOI substrate toward the lowersurface of the piezoelectric body 10, by deep reactive ion etching (DeepRIE) or the like. The SOI substrate may be etched until the lowersurface of the embedded oxide film 42 is exposed from the bottom surface142 of the recess 141, the SOI substrate may be etched until the lowersurface of the active layer 43 is exposed, or the SOI substrate may beetched until the amorphous layer 30 is exposed. Alternatively, the SOIsubstrate and the amorphous layer 30 may be etched until thepiezoelectric body 10 and the lower electrode 21 are exposed. It ispreferable to set a depth of the recess 141 such that the neutral planewithin the flexural vibration membrane is present outside thepiezoelectric body 10 when the flexural vibration membrane bends andvibrates. For example, the piezoelectric device according to the firstpreferred embodiment can be obtained by the manufacturing methodincluding the above steps.

With the existing technique, when manufacturing a piezoelectric devicehaving a flexural vibration membrane, as illustrated in FIG. 10, anamorphous film 230 is formed on a support substrate 240, a lowerelectrode 221 is formed on the amorphous film 230 by epitaxial growth,and then a piezoelectric body 210 made of aluminum nitride (AlN), leadzirconate titanate (PZT), or the like is formed by, for example, a vapordeposition method, a sputtering method, a laser ablation method, achemical vapor deposition (CVD) method, or the like, an upper electrode222 is formed on the piezoelectric body 210, and thereafter, a recess341 is formed in the support substrate 240. Therefore, in the lowerelectrode 221, distortion of a crystal lattice is reduced at a portioncloser to the piezoelectric body 210 so that a local stress is small,and in the upper electrode 222, distortion of a crystal lattice isreduced at a portion farther away from the piezoelectric body 210 sothat a local stress is small.

As such, in the piezoelectric device illustrated in FIG. 10, thedistortion of the crystal lattice of the lower electrode 221 and theupper electrode 222 varies asymmetrically with respect to thepiezoelectric body 210. Accordingly, in the piezoelectric deviceillustrated in FIG. 10, in a portion which can bend and vibrate, astress distribution is asymmetric, warpage tends to be generated,vibration efficiency is poor, and cracks and interfacial peeling tend tooccur. In the piezoelectric device illustrated in FIG. 10, when anadhesion layer is formed on the upper surface of the lower electrode221, crystallinity of the piezoelectric body 210 to be formed thereafteris deteriorated.

In contrast, in the piezoelectric device according to the firstpreferred embodiment illustrated in FIG. 1 to FIG. 3, as describedabove, the distortion in the crystal lattice of the lower electrode 21and the upper electrode 22 varies symmetrically with the piezoelectricbody 10 interposed therebetween. Accordingly, in the piezoelectricdevice according to the first preferred embodiment, in a portion whichcan bend and vibrate, a stress distribution is symmetrical, warpage ishardly generated, vibration efficiency is good, and cracks andinterfacial peeling are hardly generated. Further, in the piezoelectricdevice according to the first preferred embodiment, even though there isthe lower adhesion layer between the lower electrode 21 and thepiezoelectric body 10, the crystallinity of the piezoelectric body 10 isnot affected. Therefore, according to the first preferred embodiment, itis possible to provide a piezoelectric device having high reliabilityand a method of manufacturing a piezoelectric device.

Second Preferred Embodiment

In a second preferred embodiment of the present invention and thefollowing preferred embodiments, descriptions of the same matters asthose in the first preferred embodiment will be omitted, and onlydifferent points will be described. In particular, similar advantageousoperational effects with the same or similar configuration will not bedescribed for each preferred embodiment. As illustrated in FIG. 11, in apiezoelectric device according to the second preferred embodiment, asupport substrate is preferably a silicon substrate, for example. Thepiezoelectric device according to the second preferred embodimentincludes a recess 151 extending from a lower surface of the supportsubstrate 50 toward the lower surface of the piezoelectric body 10. Theamorphous layer 30 is exposed from a bottom surface 152 of the recess151.

Even in the second preferred embodiment, when a voltage is applied tothe piezoelectric body 10 from the lower electrode 21 and the upperelectrode 22, the piezoelectric body 10 tends to expand and contract inthe in-plane direction, but the upper electrode 22, the lower electrode21, and the amorphous layer 30 do not expand and contract, so that theflexural vibration membrane bends and vibrates vertically. It ispreferable that the thickness of the amorphous layer 30 is set such thatthe neutral plane is within the amorphous layer 30 and not within thepiezoelectric body 10 when the flexural vibration membrane bends andvibrates.

Next, a non-limiting example of a method of manufacturing thepiezoelectric device according to the second preferred embodiment willbe described.

As in the first preferred embodiment, as illustrated in FIG. 12, thelower electrode 21 is formed on the lower surface of the substratepiezoelectric body 15 by heteroepitaxial growth, and further theamorphous layer 30 is formed on the lower surface of the piezoelectricbody 15 and the lower surface of the lower electrode 21. Further, asilicon substrate is prepared as the support substrate 50. Next, asillustrated in FIG. 13, an upper surface of the silicon substrate andthe lower surface of the amorphous layer 30 are directly bonded to eachother. Thereafter, as illustrated in FIG. 14, the substratepiezoelectric body 15 is polished from the upper surface side to bethinned to form a film.

As illustrated in FIG. 15, the upper electrode 22 is formed on the uppersurface of the piezoelectric body 10 by the heteroepitaxial growth.Next, the recess 151 using the lower surface of the amorphous layer 30as the bottom surface 152 illustrated in FIG. 11 is formed from aportion of the lower surface of the silicon substrate toward thepiezoelectric body 10 by Deep RIE or the like. For example, thepiezoelectric device according to the second preferred embodiment can beobtained by the manufacturing method including the above steps. Notethat when forming the amorphous layer 30, the thickness of the amorphouslayer 30 may be set to a thickness such that the flexural vibrationmembrane to be formed thereafter can bend and vibrate, or when formingthe recess 151, the thickness of the amorphous layer 30 may be set to athickness such that the flexural vibration membrane can bend andvibrate.

Third Preferred Embodiment

As illustrated in FIG. 16, a piezoelectric device according to a thirdpreferred embodiment of the present invention further includes a supportfilm 70 covering the upper surface of the piezoelectric body 10 and theupper electrode 22. As a material of the support film 70, polysilicon,silicon nitride, aluminum nitride, and the like, for example, maypreferably be used. In the third preferred embodiment, the support film70 also defines a portion of the flexural vibration membrane. In thismanner, the support film 70 covers the upper surface of thepiezoelectric body 10, such that the support film 70 defines andfunctions as a protective film for the outside air.

In the third preferred embodiment, when a voltage is applied to thepiezoelectric body 10 from the lower electrode 21 and the upperelectrode 22, the piezoelectric body 10 tends to expand and contract inthe in-plane direction, but the support film 70, the upper electrode 22,the lower electrode 21, and the amorphous layer 30 do not expand andcontract, so that the flexural vibration membrane bends and vibratesvertically. It is preferable that a thickness of the support film 70 isset such that the neutral plane is within the support film 70 and notwithin the piezoelectric body 10 when the flexural vibration membranebends and vibrates.

Next, a non-limiting example of a method of manufacturing thepiezoelectric device according to the third preferred embodiment will bedescribed.

As in the first preferred embodiment, as illustrated in FIG. 17, thelower electrode 21 is formed on the lower surface of the substratepiezoelectric body 15, and the amorphous layer 30 is formed on the lowersurface of the piezoelectric body 15 and the lower surface of the lowerelectrode 21. Further, a silicon substrate is prepared as the supportsubstrate 50. Next, as illustrated in FIG. 18, the upper surface of thesilicon substrate and the lower surface of the amorphous layer 30 aredirectly bonded to each other. Thereafter, as illustrated in FIG. 19,the substrate piezoelectric body 15 is polished from the upper surfaceside to be thinned to form a film.

As illustrated in FIG. 20, the upper electrode 22 is formed on the uppersurface of the piezoelectric body 10. Next, as illustrated in FIG. 21,the support film 70 for covering the upper surface of the piezoelectricbody 10 and the upper electrode 22 is formed. Optionally, portions ofthe amorphous layer 30, the piezoelectric body 10, and the support film70 may be removed by an etching method or the like, thus being patternedinto a desired shape. Next, the recess 151 using the lower surface ofthe amorphous layer 30 as the bottom surface 152 illustrated in FIG. 16is formed from a portion of the lower surface of the silicon substratetoward the piezoelectric body 10 by Deep RIE or the like. Note that aportion of the amorphous layer 30 may also be removed to expose thelower electrode 21 and the lower surface of the piezoelectric body 10 tothe bottom surface of the recess 151.

According to the method of manufacturing the piezoelectric deviceaccording to the third preferred embodiment, since the support film 70is formed after the bonding between the support substrate 50 and theamorphous layer 30 and the polishing step of the piezoelectric body 10,the piezoelectric device may be manufactured more easily. In addition,it is possible to adjust the thickness of the support film 70 inaccordance with a polishing state of the piezoelectric body 10.

Fourth Preferred Embodiment

As illustrated in FIG. 22, a piezoelectric device according to a fourthpreferred embodiment of the present invention has the same orsubstantially the same configuration as that of the piezoelectric deviceaccording to the first preferred embodiment, but at least the handlelayer 41, the active layer 43, and the piezoelectric body 10 each have avariation in a thickness direction. A surface of the handle layer 41 isprovided with an unevenness, and flatness (TTV: Total ThicknessVariation) of the surface of the handle layer 41 is preferably, forexample, equal to or more than about 0 nm and equal to or less thanabout 2 μm, and more preferably equal to or more than about 0 nm andequal to or less than about 1 μm. A surface of the active layer 43 isprovided with an unevenness along the unevenness of the surface of thehandle layer 41. However, the variation in the thickness direction ofthe active layer 43 is smaller than the variation in the thicknessdirection of the handle layer 41. As such, a value of TTV of the surfaceof the active layer 43 becomes smaller than a value of TTV of thesurface of the handle layer 41. A surface of the piezoelectric body 10is provided with an unevenness along the unevenness of the surface ofthe handle layer 41 and the active layer 43. However, the variation inthe thickness direction of the piezoelectric body 10 is smaller than thevariation in the thickness direction of the active layer 43. As such,the value of TTV of the surface of the piezoelectric body 10 becomessmaller than the value of TTV of the surface of the active layer 43.

Next, a non-limiting example of a method of manufacturing thepiezoelectric device according to the fourth preferred embodiment willbe described.

As illustrated in FIG. 23, the handle layer 41 preferably made of, forexample, silicon is prepared, and an upper surface and the lower surfaceof the handle layer 41 are polished or etched in a manner such that theTTV becomes a predetermined value, thus forming the unevenness on theupper surface and the lower surface of the handle layer 41. For example,when the handle layer 41 preferably has a diameter of about 4 inches,about 6 inches, or about 8 inches, the upper surface and the lowersurface of the handle layer 41 are treated such that the TTV ispreferably, for example, equal to or more than about 0 nm and equal toor less than about 2 μm, and more preferably equal to or more than about0 nm and equal to or less than about 1 μm.

The handle layer 41 is thermally oxidized, and the oxide film 42 isformed on the upper surface of the handle layer 41 as illustrated inFIG. 24. An uneven shape is also formed on the surface of the oxide film42 according to an uneven shape of the surface of the handle layer 41.Thereafter, as illustrated in FIG. 25, the handle layer 41 on which theoxide film 42 is provided and the silicon substrate 143 are bonded eachother by fusion bonding or the like.

The silicon substrate 143 is made to be a thin film by grinder machiningor chemical-mechanical polishing (CMP), and the active layer 43 isformed on the oxide film 42 as illustrated in FIG. 26. With this, thesupport substrate 40 is formed, which is preferably, for example, asilicon on insulator (SOI) substrate including the handle layer 41, theembedded oxide film 42 disposed on the handle layer 41, and the activelayer 43 disposed on the embedded oxide film 42. When the siliconsubstrate 143 is made to be a thin film, the lower surface of the handlelayer 41 is used as a reference surface, so that an uneven shape is alsoformed on the upper surface of the active layer 43. However, the valueof TTV in the active layer 43 becomes smaller than the value of TTV inthe handle layer 41.

As in the first preferred embodiment, as illustrated in FIG. 27, thelower electrode 21 is formed on the lower surface of the substratepiezoelectric body 15 by the heteroepitaxial growth, and the amorphouslayer 30 is formed on the lower surface of the piezoelectric body 15 andthe lower surface of the lower electrode 21.

As illustrated in FIG. 28, the upper surface of the active layer 43 ofthe SOI substrate and the lower surface of the amorphous layer 30 aredirectly bonded to each other. Before bonding, a layer made of the samematerial as that of the amorphous layer 30 or a layer made of a metalmay be formed on the upper surface of the active layer 43.

As illustrated in FIG. 29, the substrate piezoelectric body 15 ispolished from the upper surface side to be thinned, thus forming thepiezoelectric body 10 as a film. At this time, by using the lowersurface of the handle layer 41 as a reference surface, an uneven shapeis also formed on the upper surface of the piezoelectric body 10.However, the value of TTV in the piezoelectric body 10 becomes smallerthan the value of TTV in the handle layer 41. Alternatively, the uppersurface of the piezoelectric body 10 may be flattened.

As in the first preferred embodiment, as illustrated in FIG. 30, theupper electrode 22 is formed on the upper surface of the piezoelectricbody 10. Thereafter, the recess 141 illustrated in FIG. 22 is formedfrom a portion of the lower surface of the handle layer 41 of the SOIsubstrate toward the lower surface of the piezoelectric body 10 by deepreactive ion etching (Deep RIE) or the like, as in the first preferredembodiment. The bottom surface 142 of the recess 141 formed by etchingbecomes flat.

According to the method of manufacturing the piezoelectric deviceaccording to the fourth preferred embodiment, it is possible to easilymanufacture the piezoelectric device in which the TTV of the activelayer 43 and the piezoelectric body 10 is smaller than the TTV of thehandle layer 41. Since the TTV of the active layer 43 and thepiezoelectric body 10 is small, a TTV of the flexural vibration membraneto be formed is reduced, and characteristics of the piezoelectric deviceare improved.

Fifth Preferred Embodiment

In a piezoelectric device according to a fifth preferred embodiment ofthe present invention illustrated in FIG. 31, although the handle layer41 has the variation in the thickness direction as in the fourthpreferred embodiment, the upper surface of the active layer 43 is flat,and the upper surface and the lower surface of the piezoelectric body 10are also flat. When manufacturing the piezoelectric device according tothe fifth preferred embodiment, the handle layer 41 provided with theoxide film 42 and the silicon substrate 143 are bonded by fusion bondingor the like as in the fourth preferred embodiment, and then the uppersurface of the active layer 43 may be flattened when making the siliconsubstrate 14 be a thin film to form the active layer 43.

As described above, the piezoelectric devices and the methods ofmanufacturing the piezoelectric devices according to each preferredembodiment of the present invention have the following configuration andadvantageous operational effects as an example in accordance with thecombination of any one or more of the above.

The piezoelectric devices according to preferred embodiments of thepresent invention each include the piezoelectric body 10 at least aportion of which can bend and vibrate, the upper electrode 22 which isdisposed on the upper surface of the piezoelectric body 10 and in whichdistortion of the crystal lattice is reduced as a distance from theupper surface of the piezoelectric body 10 increases, the lowerelectrode 21 which is disposed on the lower surface of the piezoelectricbody 10 and in which distortion of the crystal lattice is reduced as adistance from the lower surface of the piezoelectric body 10 increases,and the support substrate 40 disposed below the piezoelectric body 10.The piezoelectric device is provided with the recess 141 extending fromthe lower surface of the support substrate 40 toward the lower surfaceof the piezoelectric body 10.

In the piezoelectric device having a MEMS structure, a thickness of eachof the upper electrode 22 and the lower electrode 21 is not negligiblein the flexural vibration membrane. As such, the flexural vibrationmembrane is easily affected by a stress distribution in the upperelectrode 22 and the lower electrode 21. However, in the piezoelectricdevices according to preferred embodiments of the present invention, thedegree of distortion in the crystal lattice of the lower electrode 21and the upper electrode 22 changes symmetrically with the piezoelectricbody 10 interposed therebetween. Therefore, in the piezoelectric devicesaccording to preferred embodiments of the present invention, the stressdistribution is symmetrical in a portion which can bend and vibrate,warpage is hardly generated, vibration efficiency is good, and cracksand interfacial peeling are hardly generated.

In the piezoelectric devices described above, a plurality of layers ofthe piezoelectric body 10 may be included, the plurality of layers mayinclude an upper layer and a lower layer, the upper electrode 22 may bedisposed on the upper surface of the piezoelectric body of the upperlayer, and the lower electrode 21 may be disposed on the lower surfaceof the piezoelectric body of the lower layer.

According to this, it is possible to obtain a large displacement inflexural vibration by using a bimorph structure.

In the piezoelectric devices described above, the upper electrode 22 andthe lower electrode 21 may have at least one or more kinds of triaxialtextures. In the piezoelectric device described above, the upperelectrode 22 and the lower electrode 21 may have one kind of triaxialtexture.

According to this, performance of the piezoelectric device is improved.When the upper electrode 22 and the lower electrode 21 have one kind oftriaxial texture, power durability is improved.

In the piezoelectric devices described above, the piezoelectric body 10may be made of a single crystal. The piezoelectric body 10 may be madeof lithium tantalate or lithium niobate.

According to this, since the piezoelectric body 10 is a single crystal,a polarization state is uniform, and since there is no grain boundary inthe piezoelectric body 10, a stress distribution is hardly generated inthe piezoelectric body 10, so that cracks and leaks are hardlygenerated.

In addition, according to preferred embodiments of the presentinvention, the methods of manufacturing the piezoelectric devices inwhich at least a portion of the piezoelectric body can bend and vibrateincludes depositing a conductive material on the lower surface of thepiezoelectric body 15 to form the lower electrode 21 made of a depositedconductive material, depositing a conductive material on the uppersurface of the piezoelectric body 10 to form the upper electrode 22 madeof a deposited conductive material, disposing the support substrate 40below the piezoelectric body 10, and providing the recess 141 extendingfrom the lower surface of the support substrate 40 toward the lowersurface of the piezoelectric body 10.

In the piezoelectric devices manufactured by the manufacturing methodsaccording to preferred embodiments of the present invention, thecrystallinity of the lower electrode 21 and the upper electrode 22varies symmetrically with the piezoelectric body 10 interposedtherebetween. Therefore, in the piezoelectric devices manufactured bythe manufacturing methods according to preferred embodiments of thepresent invention, the stress distribution is symmetrical in a portionwhich can bend and vibrate, warpage is hardly generated, vibrationefficiency is good, and cracks and interfacial peeling are hardlygenerated.

In the methods of manufacturing the piezoelectric devices describedabove, the piezoelectric body 10 may include a plurality of layers, andthe plurality of layers may include the upper layer and the lower layer,the lower electrode 21 may be formed on the lower surface of thepiezoelectric body of the lower layer, and the upper electrode 22 may beformed on the upper surface of the piezoelectric body of the upperlayer.

According to this, since the piezoelectric device having the bimorphstructure is manufactured, it is possible to obtain a large displacementin the flexural vibration of the piezoelectric device to bemanufactured.

In the methods of manufacturing the piezoelectric devices describedabove, the upper electrode 22 and the lower electrode 21 may be formedby epitaxially growing a conductive material.

According to this, the distortion of the crystal lattice of the upperelectrode 22 and the lower electrode 21 is made to be symmetrical but begood, and the performance of the piezoelectric device is improved.

In the methods of manufacturing the piezoelectric devices describedabove, the lower electrode 21 may be formed on the lower surface of thepiezoelectric body 15 with a lower adhesion layer made of a metalinterposed therebetween.

According to this, adhesiveness between the piezoelectric body 10 andthe lower electrode 21 is improved in the piezoelectric device to bemanufactured, and reliability of the piezoelectric device is improved.

In the methods of manufacturing the piezoelectric devices describedabove, the upper electrode 22 may be formed on the upper surface of thepiezoelectric body 10 with an upper adhesion layer made of a metalinterposed therebetween.

According to this, adhesiveness between the piezoelectric body 10 andthe upper electrode 22 is improved in the piezoelectric device to bemanufactured, and the reliability of the piezoelectric device isimproved.

In the methods of manufacturing the piezoelectric devices describedabove, the piezoelectric body 15 may be made of a single crystal.Alternatively, the piezoelectric body 15 may be made of lithiumtantalate or lithium niobate.

According to this, since the piezoelectric body 10 is a single crystalin the piezoelectric device to be manufactured, there is no need toperform polarization treatment of the piezoelectric body 15 afterforming the upper electrode 22 and the lower electrode 21, and sincethere is no grain boundary in the piezoelectric body 10, stress ishardly generated in the piezoelectric body 10, so that cracks and leaksare hardly generated.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A piezoelectric device comprising: apiezoelectric body at least a portion of which is capable of bending andvibrating; an upper electrode which is disposed on an upper surface ofthe piezoelectric body and in which distortion of a crystal lattice isreduced as a distance from the upper surface increases; a lowerelectrode which is disposed on a lower surface of the piezoelectric bodyand in which distortion of a crystal lattice is reduced as a distancefrom the lower surface increases; and a support substrate disposed belowthe piezoelectric body; wherein a recess extending from a lower surfaceof the support substrate toward the lower surface of the piezoelectricbody is provided.
 2. The piezoelectric device according to claim 1,wherein a plurality of layers of the piezoelectric body are included;the plurality of layers include an upper layer and a lower layer; theupper electrode is disposed on an upper surface of the upper layer; andthe lower electrode is disposed on a lower surface of the lower layer.3. The piezoelectric device according to claim 1, wherein the upperelectrode and the lower electrode include at least one or more kinds oftriaxial textures.
 4. The piezoelectric device according to claim 1,wherein the upper electrode and the lower electrode include one kind oftriaxial texture.
 5. The piezoelectric device according to claim 1,further comprising a lower adhesion layer made of a metal between thepiezoelectric body and the lower electrode.
 6. The piezoelectric deviceaccording to claim 1, further comprising an upper adhesion layer made ofa metal between the piezoelectric body and the upper electrode.
 7. Thepiezoelectric device according to claim 1, wherein the piezoelectricbody is made of a single crystal.
 8. The piezoelectric device accordingto claim 1, wherein the piezoelectric body is made of lithium tantalateor lithium niobate.
 9. The piezoelectric device according to claim 1,further comprising an amorphous layer disposed on the lower surface ofthe piezoelectric body and on a lower surface of the lower electrode.10. The piezoelectric device according to claim 9, wherein the amorphouslayer is made of silicon oxide.
 11. The piezoelectric device accordingto claim 1, wherein the upper surface and the lower surface of thepiezoelectric body are flat and smooth such that a Total ThicknessVariation is equal to or less than about 2 μm.
 12. A method ofmanufacturing a piezoelectric device in which at least a portion of apiezoelectric body is capable of bending and vibrating, the methodcomprising: depositing a conductive material on a lower surface of thepiezoelectric body to form a lower electrode made of the depositedconductive material; depositing a conductive material on an uppersurface of the piezoelectric body to form an upper electrode made of thedeposited conductive material; disposing a support substrate below thepiezoelectric body; and providing a recess extending from a lowersurface of the support substrate toward the lower surface of thepiezoelectric body.
 13. The method of manufacturing the piezoelectricdevice according to claim 12, wherein the piezoelectric body includes aplurality of layers; the plurality of layers includes an upper layer anda lower layer; the lower electrode is formed on a lower surface of thelower layer; and the upper electrode is formed on an upper surface ofthe upper layer.
 14. The method of manufacturing the piezoelectricdevice according to claim 12, wherein the upper electrode and the lowerelectrode are formed by epitaxially growing the conductive material. 15.The method of manufacturing the piezoelectric device according to claim12, wherein the lower electrode is formed on the lower surface of thepiezoelectric body with a lower adhesion layer made of a metalinterposed between the lower electrode and the piezoelectric body. 16.The method of manufacturing the piezoelectric device according to claim12, wherein the upper electrode is formed on the upper surface of thepiezoelectric body with an upper adhesion layer made of a metalinterposed between the upper electrode and the piezoelectric body. 17.The method of manufacturing the piezoelectric device according to claim12, wherein the piezoelectric body is made of a single crystal.
 18. Themethod of manufacturing the piezoelectric device according to claim 12,wherein the piezoelectric body is made of lithium tantalate or lithiumniobate.
 19. The method of manufacturing the piezoelectric deviceaccording to claim 13, wherein the upper electrode and the lowerelectrode include at least one or more kinds of triaxial textures. 20.The method of manufacturing the piezoelectric device according to claim13, wherein the upper electrode and the lower electrode include one kindof triaxial texture.